Method of treating a zinc bearing ore material



y 1936- T. A. MITCHELL I Q 2,039,331

METHOD OF TREATING A ZINC BEARING ORE MATERIAL Filed NOV. 5, 1954 FILTERoezczzsoucl AL ZnCl CQCI:

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grime/WM THo/vms H. MITCHELL Patented May 5, 1936 UNITED STATES IMETHODOF TREATING A ZINC BEARING ORE MATERIAL Thomas A. Mitchell, Denver,Colo., assignor to Hughes-Mitchell Processes, Incorporated, Denver,0010., a corporation of Wyoming Application November 5, 1934, Serial No.151,475

6 Claims.

This invention relates to a method of treating a zinc bearing orematerial and deriving zinc metal and zinc compounds therefrom.

An oxidized zinc ore may contain a considerable quantity of zinc oxideintermingled with various other ore materials and the gangue, and manyproblems have been faced heretofore in deriving zinc metal from such anore, and particularly if it is complex in its nature. For example, ahigh content of lead in a roasted zinc sulfide ore makes it difficult tosmelt the ore by standard procedure and to recover zinc metal therefrom.

A primary object of this invention is to provide an economical andeflicient method of treating an ore material containing zinc oxidetogether With other compounds for the production of zinc metal or zincoxide.

A further object is to provide a cyclic process of treating an orematerial containing zinc oxide, which involves a preliminaryhydrometallurgical procedure combined with a reduction furnace step thatcooperate with one another and result in the economical production ofzinc metal. Various other objects will be apparent in' the followingdisclosure.

Referring to the drawing, I have there shown as a flow diagram thevarious steps required for deriving zinc metal from a zinc sulfide or'eor other material containing zinc oxide; but it is to be understood thatthe primary features of this invention may be employed for the treatmentof various other types of zinc bearing material,

and that the various steps of the process may be suitably modified inaccordance with the nature of the substance being treated.

Assuming that the ore is a complex ore containing zinc sulfideassociated with other materials, such as iron and lead sulfides togetherwith the usual gangue, this ore may be roasted in accordance withstandard procedure to develop a considerable amount of zinc oxidetherein and, if desired, the process of the prior patent to Mitchell No.1,943,331 of January 16, 1934 may be adopted in so far as it applies tothe present process, and particularly where the ore tends to sintereasily during the roasting operation or where it is desired to convertthe major portion of the-zinc sulfide to zinc oxide and to obtain apulverulent material which may be readily treated by fluid reagents. It,however, is to be understood that various other types of roastingoperations may be employed within the scope of t is invention, and thatif zinc sulfate is formed,

it will be readily converted to zinc chloride byZnO+CaClz+COz=ZnClz+CaCO3 In accordance therewith, I propose to treatthe oxidized ore material, and preferably while still hot as it comesfrom the roaster, with a solution of an alkaline earth metal chloride,such as barium, strontium or calcium chloride, and in the presence ofcarbon dioxide gas. This step results in the conversion of zinc oxide tozinc chloride with the precipitation of alkaline earth metal carbonate,although an excess of alkaline earth metal chloride may remain, ifdesired, in the solution. This particular procedure is preferablycarried out in an absorption tower, in which the roasted ore material orother zinc oxide bearing material employed in the process is in a finelydivided condition, and preferably one which will pass through a screenof meshes to the linear inch. Ordinarily, I use'cal- .cium chloride asthe chlorine bearing reagent and in a strong aqueous solution. The orematerial together with the calcium chloride solution is preferablypassed downwardly over a series of baflles in a high absorption tower,while carbon dioxide gas is maintained in the absorption tower under asufiiciently high pressure to insure an efficient reaction. If desired,the absorption tower may be jacketed and heated to any suitabletemperature by an externally heated gas, such as may be derived from theroaster. Also, various provisions will be employed to insure that theresultant zinc chloride solution is of a sufiiciently high concentrationfor the purpose. This may be obtained by passing the sludge of oreparticles and solution repeatedly over the bailies of the tower by meansof a recirculating pump, and the operation will be kept up until thezinc chloride solution is-of a sufficiently high concentration. Also,the temperature and pressure on the gas will be so regulated as torender'the process efficient. It is preferred to have the temperature ofthe solution near the boiling point and to apply sufficient pressure onthe gas, such as one atmosphere or more, to insure that a considerablevolume thereof is in intimate contact with the ore sludge. If zincsulfate is formed during the roasting operation, or is present for otherreasons, the alkaline earth metal chloride will react directly therewithand form zinc chloride together with a precipitate of alkaline earthmetal sulfate. Hence, it is not necessary to roast a sulfide ore whollyto the oxide condition. In this way, it is easy to obtain a zincchloride solution which has a strength as high as 50 B.

When the zinc chloride solution has been made sufiiciently strong, thenthe ore residue and solution are passed through a suitable filter orother separating apparatus which serves to withdraw the solution fromthe ore residue, and the latter may then be treated as desired. The zincchloride solution, which may contain calcium chloride, may now betreated in any suitable manner to purify it from undesired elements, asis determined by chemical analysis and in accordance with the nature ofthe material being treated. Any suitable and standard procedure may beadopted for this purpose.

The next primary feature of the invention involves the chemical reactionof:

In accordance with this equation, calcium sulfide or other alkalineearth metal sulfide, such as barium or strontium sulfide, has thecapacity of precipitating zinc sulfide from its chloride solution. Itwill be understood that if calcium chloride is used in the first stage,then calcium will preferably be used at this point. It is likewisedesirable to employ barium or strontium sulfides at this stage if theirchlorides were used in the preliminary chloridizing operation, althoughone may use two different metal ions, if desired. The process isdescribed herein as involving the use of calcium compounds only.

In order to carry out this second stage step, it is preferred that thecalcium sulfide be present in a finely divided condition, and that it besuspended initially in a solution of calcium chloride of high strengthso as not to dilute the reacting solutions unnecessarily. Then, thissuspension of calcium sulfide is introduced into the solution of zincchloride of high strength, and the mixture is thoroughly agitated, withthe result that zinc sulfide is formed as a precipitate and calcium goesinto solution as calcium chloride. If the initial zinc chloride solutionwere of 50 Beaum, the resulting calcium chloride solution may be' ofapproximately 40 B. This means that the calcium chloride solution is,therefore, in condition for re-use in-the process without evaporation ofits water content, or it is available for other purposes. It, of course,is feasible to regulate the concentration of the solutions as desired.

It will now be appreciated that I have provided a very simple procedurefor forming zinc sulfide from a zinc sulfide ore or any zinc oxidematerial, and this zinc sulfide may be recovered and utilized as anarticle of commerce or otherwise treated. I

In case it is desired to produce zinc metal or zinc oxide, this may beaccomplished by heating the zinc sulfide with lime and carbon. To thisend, the zinc sulfide is separated from its calcium chloride solution ona suitable filter, and the zinc sulfide may be washed or otherwisetreated to remove the undesired solution therefrom. The zinc'sulfide maynow be mixed with lime and coke which are proportioned to react inaccordance with the following equation:

ZnS+CaO+C:Zn+CaS+CO The lime, carbon and zinc sulfide may be mixed inthe proportions of 59% ZnS, 34% CaO and 7% carbon, as measured byweight. Various procedures may be adopted for mixing the material, whichmay be accomplished with the zinc sulfide either wet or dry. One simplemethod is to take the wet zinc sulfide as it comes from the filter andwashing steps and mix it intimately with lime and coke in the propermolecular proportions, or with the reagents in excess if desired, andthen to form small briquettes of theingredients. These are thenintroduced into a suitable reduction furnace, and heat as is required isapplied to cause the conversion of the zinc compound to the metal.

It will be appreciated that this reduction proc-- ess involves aself-contained reaction in which the oxygen content of the lime and thecarbon are present in amount sufiicient to free the calcium and permitit to react with the zinc sulfide to form calcium sulfide and leavemetallic zinc. This reaction does not require an excessive amount ofcarbon, as would be necessary if one were reducing zinc sulfate insteadof zinc sulfide. Also, if alkaline earth metal sulfide remains in excesswith the zinc sulfide, this will not matter and particularly if one usesthe oxide of the same metal as was used in making the zinc sul- Thecarbon monoxide gas given off from this furnace may be now oxidized tocarbon dioxide by burning the same in air, and this carbon dioxide isthen available for returning to .the first absorber stage, as isindicated on the drawing. Thus, the process is cyclic with regard to thecarbon dioxide evolved from the reduction furnace. It is also to beunderstood that the ore residue containing the calcium carbonate, asderived from the first absorber stage, may be treated with dilutehydrochloric acid to decompose the calcium carbonate and re-form carbondioxide for further use in the process, as well as calcium chloride insolution, which may be likewise returned to process.

The reduction furnace may be of any suitable construction, and thisparticular phase of the process may be carried on in accordance with therequirements; butit is preferable that the furnace temperature besumciently high so that the zinc will be evolved in a vapor conditionand condensed in a suitably cooled zone outside of the reduction zone.This serves to separate the zinc from the residue of calcium sulfide andleaves the latter free for return to process, as indicated on thedrawing. The zinc fumes, after being caught in a condenser, may bemolded into slab formor otherwise recovered. If desired, the zinc fumesmay be oxidized by the admission of air to the hot fumes which serves toburn the same to zinc oxide. The zinc oxide may be recovered by means ofa baghouse of suitable design.

It will now be appreciated that these various steps cooperate towards auseful result. In this way, I have provided a process whereby aconsiderable proportion of the zinc content of an ore may be firstconverted to zinc oxide and then to zinc sulfide, and finally to zincmetal by a series of steps in which compounds of an alkaline metal areutilized in all of the stages, and in which various compounds employedas reagents are used and recovered cyclically in the process. Theeconomical advantages of this procedure will be readily apparent. I

Having thus described the invention, what is claimed as new and desiredto secure by Letters Patent is:

1. The method of recovering zinc from an ore material containing zincoxide comprising the steps of treating the material in finely dividedcondition with a solution of alkaline earth metal chloride and carbondioxide and forming zinc chloride, separating the resultant solutionfrom the ore residue and treating it with sufficient alkaline earthmetal sulfide to precipitate the zinc as a sulfide, and thereafterheatingthe zinc sulfide with alkaline earth metal oxide and carbon toreduce the zinc sulfide to zinc metal and form alkaline earth metalsulfide, and separating the zinc from the furnace residue.

2. The method of claim 1 in which compounds of the same alkaline earthmetal are employed as reagents at the various stages, whereby thealkaline earth metal chloride and sulfide may be returned for cyclic usein the process.

3. The method of making zinc sulfide from a raw ore containing the samecomprising the steps of roasting the ore and producing a finely dividedore material containing zinc oxide, treating the product with a solutionof an alkaline earth metal chloride and carbon dioxide and producing asolution of zinc chloride of high concentration, treating the zincchloride solution with alkaline earth metal sulfide in amount suflicientto precipitate all of the zinc as a sulfide, and thereafter separatingthe zinc sulfide from the solution, said alkaline earth metal sulfidebeing initially suspended in a strong solution of the chloride of thesame alkaline earth metal as was used in the chloridizing step, wherebythe resultant solution will be 01 high strength and capable of reuse inthe process. 7 v

4, The method of making zinc from a raw ore containing the samecomprising the steps of roasting the ore and producing a finely dividedore may terial containing zinc oxide, treating the product with asolution of an alkaline earth metal chloride 5. The method of claim 1 inwhich the zinc -metal is volatilized by heat and thus separated from thefurnace residue, after which the fumes are treated with air to form zincoxide.

6. The method of treating an oxidized ore material containing zinc oxidecomprising the steps of converting the zinc oxide to a chloride bytreating the ore in finely divided condition with calcium chloride in astrong aqueous solution and carbon dioxide gas, and continuing thetreatment until a strong solution of zinc chloride is obtained,separating this solution from the ore residue, treating the solutionwith calcium sulfide suspended therein and proportioned to precipitatethe zinc as zinc sulfide, separating the precipitate from the solution,mixing it in stoichiometric proportions with lime and carbon forproducing zinc, and heating the mixture to produce zinc as a vapor whichis thus distilled from the residue and recovered.

THOMAS A. MITCHELL.

